1. Field of the Invention
The present invention generally relates to a method and apparatus for monitoring conditions downhole and/or manipulating downhole tools. More particularly, the present invention relates to a method and apparatus for monitoring conditions downhole and/or manipulating downhole tools while placing wire which connects the surface to downhole onto a casing string while drilling with casing. Even more particularly, the present invention relates to a method and apparatus for wiring casing while drilling with casing.
2. Description of the Related Art
In conventional well completion operations, a wellbore is formed to access hydrocarbon-bearing formations by the use of drilling. In drilling operations, a drilling rig is supported by the subterranean formation. A rig floor of the drilling rig is the surface from which casing strings, cutting structures, and other supplies are lowered to form a subterranean wellbore lined with casing. A hole is formed in a portion of the rig floor above the desired location of the wellbore. The axis that runs through the center of the hole formed in the rig floor is well center.
Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill support member, commonly known as a drill string. The drill string includes sections of drill pipe threadedly connected to one another, often connected at the drilling rig by a pipe handling operation. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on the drilling rig. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore.
Often, it is necessary to conduct a pipe handling operation to connect sections of casing to form a casing string which extends to the drilled depth. Pipe handling operations require the connection of a first casing section to a second casing section to line the wellbore with casing. To threadedly connect the casing strings, each casing section must be retrieved from its original location, typically on a rack beside the drilling platform, and be suspended above well center so that each casing section is in line with the casing section previously disposed within the wellbore. The threaded connection must be made up by a device that imparts torque to one casing section relative to the other, such as a power tong or a top drive. The casing string formed of the two casing sections is then lowered into the previously drilled wellbore.
Technology is available which allows communication in real time between the surface of the wellbore and within the wellbore while drilling with the drill string, often termed “measurements while drilling”. One data transmission method from downhole to the surface while drilling with the drill string is mud pulsing, which involves digitally encoding data and transmitting the data to the surface as pressure pulses in the mud system. Communication between the surface and downhole permits sensing of conditions within the wellbore, such as pressure, formation, temperature, or drilling fluid parameters. By monitoring the conditions within the wellbore in real time while drilling with the drill string, conditions may be adjusted and optimized accordingly. The mud pulsing method of data transmission is disadvantageously slow and capable of transmitting little or no power or data.
Another method for data transmission in real time through drill pipe while drilling with the drill string involves drilling with wires or cables. Employing wires or cables which connect surface equipment and downhole equipment located within the wellbore allows operation of downhole equipment by sending signals or power from the surface to downhole equipment. Exemplary downhole equipment which may be advantageously operated from the surface includes a motor which provides torque to the drill string for drilling into the formation as well as float equipment. Furthermore, communication between the surface and downhole allows sensing of wellbore conditions, as delineated above. A sensor may be placed close to or within the drill bit at the end of the drill string to transmit data regarding conditions present in the wellbore to the surface equipment. The surface equipment then processes the signal into interpretable data.
It is common to employ more than one string of casing in a wellbore. In this respect, the well is drilled to a first designated depth with a drill bit on a drill string. The drill string is removed. Sections of casing are connected to one another and lowered into the wellbore using the pipe handling operation described above to form a first string of casing longitudinally fixed in the drilled out portion of the wellbore. While the above method of data and power transmission in real time while initially drilling with the drill string to drill a hole for the casing string is generally more effective than mud pulsing because it allows more power and data transmission in a faster period of time, the process of drilling into the formation with the drill string to a first depth to form a wellbore for a first casing string while sensing conditions in real time, then removing the drill string from the wellbore, then placing the first casing string within the wellbore, then drilling the wellbore to a second depth with the drill string, then removing the drill string, then placing the second casing string within the wellbore, and then repeating this process for subsequent casing string is time consuming and, thus, not cost effective.
It is often desirable to monitor conditions within the wellbore or to operate tools disposed on the casing string while lowering the first casing string and/or subsequent casing strings into the wellbore. To communicate from the surface to downhole, and vice versa, a first section of wire is often connected to downhole equipment, while a second section of wire is connected to surface equipment. The first section of wire is disposed on the first casing section of the first casing string, while the second section of wire is disposed on the second casing section of the first casing string. The wires must be aligned to provide a conductive path between the surface and downhole. The usual method to align the wires of casing sections involves timing threads, wherein the threads of each casing section are machined so that at a given torque, the wires are aligned. Timing marks are usually disposed on each casing section. When the timing marks are aligned, which may be visually ascertained, the wire sections are aligned to conduct through casing sections. Methods for clocking or timing threads are described in U.S. Pat. No. 5,233,742 entitled “Method and Apparatus for Controlling Tubular Connection Make-Up”, issued on Aug. 10, 1993 to Gray et al., and in U.S. Pat. No. 4,962,579 entitled “Torque Position Make-Up of Tubular Connections”, issued Oct. 16, 1990 to Moyer et al., which are both herein incorporated by reference in their entirety.
The next step in a typical drilling operation includes cementing the first string of casing into place within the wellbore by a cementing operation. Next, the well is drilled to a second designated depth through the first casing string, and a second, smaller diameter string of casing comprising casing sections is hung off of the first string of casing. A second cementing operation is performed to set the second string of casing within the wellbore. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wellbores are typically formed with two or more strings of casing.
After the two or more strings of casing are set within the wellbore, it is often desirable to monitor conditions within the wellbore during operations such as hydrocarbon production operations or treatment operations. It is also desirable to operate downhole tools such as packers and valves from the surface during downhole operations. One method of providing communication from the surface to downhole (and vice versa) involves running wire connected to downhole equipment at one end, such as a sensor or a downhole tool, and connected to surface equipment at the other end, such as a processing unit, into the wellbore after placing the casing string into the wellbore. Another method involves placing a section of wire on each casing string as it is lowered into the previously-drilled wellbore, then inductively coupling the wire from each casing string to the wire from the adjacent casing string. In this way, the casing strings may be inductively coupled end-to-end. A method and apparatus for inductively coupling casing strings is illustrated in U.S. Pat. No. 4,901,069 issued to Veneruso on Feb. 13, 1990, which is herein incorporated by reference in its entirety.
In the conventional well completion operations described above, wire is placed on the outside of a casing section as it is lowered into the drilled out portion of the formation. Running the wire on the outside of casing sections subjects the wire to damage and degradation due to wellbore fluids, which may be turbulent in flow and/or high in temperature within the wellbore.
As an alternative to the conventional drilling method, drilling with casing is a method often used to place casing strings within the wellbore. This method involves attaching an earth removal member typically in the form of a drill bit to the lower end of the same string of casing which will line the wellbore. Drilling with casing is often the preferred method of well completion because only one run-in of the working string into the wellbore is necessary to form and line the wellbore for each casing string.
Drilling with casing may be accomplished in at least two manners. In the first method, the first casing string inserted into the wellbore has an earth removal member operatively attached to its lower end. The first casing string may include one or more sections of casing threadedly connected to one another by the pipe handling operation described above. In a drilling with casing operation, the casing sections are threaded to one another using the top drive connected to a gripping head. The gripping head has a bore therethrough through which fluid may flow and grippingly engages the casing sections to serve as a load path to transmit the full torque applied from the top drive to the casing sections to make up the connection between casing sections. The gripping head is an external gripping device such as a torque head or an internal gripping device such as a spear. An exemplary torque head is described in U.S. Pat. No. 6,311,792 B1 issued to Scott et al. on Nov. 6, 2001, which is herein incorporated by reference in its entirety. An exemplary spear is described in U.S. Patent Application Publication No. US 2001/0042625 A1, filed by Appleton on Jul. 30, 2001, which is herein incorporated by reference in its entirety.
After the pipe handling operation is conducted to connect casing sections to form a casing string, the first casing string is lowered into the formation while the earth removal member rotates to drill the first casing string to a first depth. The first casing string is then secured above the formation by a gripping mechanism such as a spider, which comprises a bowl inserted in the rig floor and gripping members such as slips which are movable within the bowl along an inclined slope to grippingly engage the outer diameter of casing strings. The gripping head is released from engagement with the first casing string.
The gripping head then grippingly and sealingly engages a second casing string. The second casing string is threadedly connected to the first casing string by a pipe handling operation. The spider is released as the gripping head now suspends the two connected casing strings, and the earth removal member on the first casing string is rotated while the first and second casing strings, which are now connected and move together, are lowered to drill the first and second casing strings to a second depth within the formation. This process is repeated to drill subsequent casing strings to a further depth within the formation.
A second drilling with casing method involves drilling with concentric strings of casing. In this method, the first casing string is run into the wellbore with a first earth removal member operatively connected to its lower end. The first earth removal member rotates relative to the first casing string as the first casing string is simultaneously lowered into the formation to drill the first casing string to a first depth. The first casing string is set by setting fluid such as cement within the wellbore. Next, a second casing string, which is smaller in diameter than the first casing string, having a second earth removal member operatively connected to its lower end, drills through the cutting structure of the first casing string and to a second depth in the formation. The second earth removal member and the second casing string drill in the same way as the first casing string. The second casing string is set within the wellbore, and subsequent casing strings with earth removal members attached thereto are drilled into the formation in the same manner as the first and second casing strings.
During the drilling with casing operation, it is necessary to circulate drilling fluid while drilling the casing string into the formation to form a path within the formation through which the casing string may travel. Failure to circulate drilling fluid while running the casing string into the formation may cause the casing string to collapse due to high pressure within the wellbore; therefore, it is necessary for a fluid circulation path to exist through the casing string being drilled into the formation. A unique condition encountered while drilling with casing is plastering. Because the casing string is rotated so close to the formation, less fluid exists around the outside of the casing string while drilling.
In both drilling with casing methods described above, after the casing string is drilled to the desired depth within the formation, the casing string must often be cemented into the wellbore at a certain depth before an additional casing string is hung off of the casing string so that the formation does not collapse onto the casing string due to lack of support. Furthermore, the casing string must be cemented into the formation once it reaches a certain depth to restrict fluid movement between formations. To cement the casing string within the wellbore, a cementing tool including a cementing head is inserted into the casing string to inject cement and other fluids downhole and to release cement plugs.
While drilling with casing, it is desirable to monitor parameters within the wellbore in real time, as well as to operate downhole tools while drilling. It would be especially advantageous to sense the extent of plastering and hydrostatic conditions in real time while drilling with casing, as the solids content of the drilling fluid and other parameters of the fluid may be monitored and optimized while the casing string is drilling to facilitate drilling the casing string into the formation. It would be further advantageous to monitor downhole tools in real time, including cementing equipment and mud motors used to rotate the casing string while drilling.
To provide communication between the surface and downhole to monitor downhole conditions and operate downhole tools, the data communication must exist through a wire connecting the surface to downhole. Currently in drilling with casing operations, the wire is run into the wellbore after insertion of all of the desired casing strings within the wellbore. Downhole equipment is run into the wellbore with the casing string, and then, after the casing string is placed within the wellbore, a wire connected at one end to surface equipment is run into the wellbore and plugged into the downhole equipment. Running the wire into the casing string after drilling the casing string into the formation does not allow real time monitoring of the wellbore conditions during drilling.
Therefore, it is desirable to produce a wired casing string which is capable of transmitting electricity through the casing string across the threadable connections of individual casing joints. It is further desirable to produce a casing string which is capable of drilling into the formation as well as cementing the casing string into the formation through communication to the downhole equipment from the surface. It is even more desirable to place wire on the casing string while drilling with the casing string into the formation to allow real time monitoring of downhole conditions and operation of downhole tools while drilling with casing. It is further desirable to protect the wire from damage within the wellbore. It is even further desirable to protect the wire from damage within the wellbore across connections of sections of casing.